In the power supply system, the current detection technology is widely applied to achieve the functions such as current control, current protection, parallel current sharing and current monitoring, so it is very important to obtain a precise current detection result. FIG. 1 is a schematic diagram of a current detection circuit in the related art. As shown in FIG. 1, the current detection circuit 12 includes an output inductor L, a sampling resistor R and a differential amplifier 122. The output inductor L and the sampling resistor R are respectively coupled to a positive pole 13 and a negative pole 14 of the power conversion circuit 11, and the power conversion circuit 11 also has an input voltage Vin and an output voltage VO. Input terminals of the differential amplifier 122 are connected in parallel to two ends of the resistor R so as to amplify a current signal at the two ends of the sampling resistor R to obtain a current detection signal. In particular, through measuring the voltage at the two ends of the sampling resistor R and using the formula I=V/R, the magnitude of the current signal at the two ends of the sampling resistor R can be obtained, and thus the magnitude of the current detection signal may be obtained.
Due to sampling current by a sampling resistor with high precise, in the above method, the sampled values are relatively stable since the resistor having low temperature coefficient can be selected to avoid the effects of the temperature drift. However, this method has the following deficiencies: the loss of the sampling resistor is large when the current flowing through the sampling resistor is relatively large, and the heat dissipation and the occupied volume should also be considered during the design process of the circuit.
FIG. 2 is a schematic circuit diagram of another DC-DC converter in the related art. As shown in FIG. 2, the current detection circuit 12 includes an output inductor 121, a sampling resistor R, a sampling capacitor C and a differential amplifier 122. The output inductor 121 includes an inductor L and an equivalent series resistor R1 of the inductor. A sampling resistor R and a sampling capacitor C are connected in series, and then connected to the output inductor 121 in parallel. Input terminals of the differential amplifier 122 are connected in parallel to two ends of the capacitor C. The output inductor 121, the sampling resistor R and the sampling capacitor C are connected to an output side of the power conversion circuit 11, and the power conversion circuit 11 also has an input voltage Vin (the input terminals are marked as 13 and 14, respectively) and an output voltage VO.
As shown in FIG. 2, if the current flowing through the inductor L is iL, the current flowing through the capacitor C is iC, the voltage at two ends of the inductor L is vL and the voltage on the capacitor C is vC, the following equation (1) is obtained: vL+iLR1=vC+iCR. The following equation (2) is obtained by averaging the equation (1) in one switching cycle: VL+ILR1=VC+ICR. In the equation (2), VL is an average value of the voltage on the inductor in one switching cycle, and obviously VL=0; VO is an average value of the output voltage; IL is an average value of the current of the inductor and equal to a load current IO; iC is an average value of the charging and discharging current of the capacitor in one switching cycle, and obviously IC=0; and R1 is an ESR (equivalent series resistance) of the inductor.
Thus, the equation (2) may be transformed into an equation (3): ILR1=VC. That is, the following equation (4) is obtained: IL=IO=VC/R1.
Therefore, it is enough for detecting the magnitude of the load current and the current of the inductor to detect the magnitude of the voltage on the capacitor. Such method may sample the current conveniently, easily and without loss.
However, this method also has the following defects: in the current detection circuit, relatively large capacitor and resistor are needed to filter the pulses flowing through the inductor L, and thus the time constant τ=R×C of the RC loop increases, the charging and discharging time becomes longer, so that it is impossible to respond to the variation of the current on the inductor L rapidly.
The above information disclosed in the part of Background is only used to enhance the understanding to the background of the present disclosure, and thus may include the information which is not the related art known by the person skilled in the art.